Magnetoresistive devices include magnetic sensors and magnetic memory devices such as magnetic random access memory (MRAM). Magnetic memory devices store information by varying the resistance across the memory device such that a read current through a memory cell in the memory device will result in a voltage drop having a magnitude that is based on the information stored in the memory cell. For example, in certain magnetic memory devices, the voltage drop across a magnetic tunnel junction (MTJ) can be varied based on the relative magnetic states of the magnetic layers within the memory cell. In such memory devices, there is typically a portion of the memory cell that has a fixed magnetic state and another portion that has a free magnetic state that is controlled to be either parallel or antiparallel to the fixed magnetic state. Because the resistance through the memory cell changes based on whether the free portion is parallel or antiparallel to the fixed portion, information can be stored by setting the orientation of the free portion. The information is later retrieved by sensing the orientation of the free portion. Such magnetic memory devices are well known in the art.
Manufacturing magnetoresistive devices, including MTJ devices, includes a sequence of processing steps during which many layers of materials are deposited and then patterned to form a magnetoresistive stack and the electrodes used to provide electrical connections to the magnetoresistive stack. The magnetoresistive stack includes the various layers that make up the free and fixed portions of the device as well as one or more dielectric layers that provide at least one the tunnel junction for the MTJ device. In many instances, the layers of material are very thin—on the order of a few or tens of angstroms. Similarly, the dimensions of such layers after patterning and etching are extremely small, and small deviations or imperfections during processing can have a significant impact on device performance.
Because an MRAM device may include millions of MTJ elements, precise processing steps used in manufacturing the devices can contribute to increased densities by allowing devices to be placed in close proximity without unwanted interaction. Moreover, such accurate processing helps to minimize deviations in device characteristics, such as switching voltages, across devices included in the MRAM. Therefore, it is desirable to provide techniques for manufacturing such devices that support increased densities and promote minimizing the variance of certain characteristics amongst devices.